Enea Bastianini ended the opening day of practice ahead of the Moto3 Aragon Grand Prix fastest from Gabriel Rodrigo, after topping the second session with a lap of 1:58.418s.
Jakub Kornfeil ended the opening 40-minute session of the day fastest of all after snatching top spot late on with a 1:59.206s, though did crash moments later.
As the track rubbered in as the session wore on, top spot changed hands frequently, with Marco Bezzecchi, his title rival and points leader Jorge Martin and Philipp Oettl all taking turns heading the pack in the opening stages.
A 2:00.725s from Leopard's Bastianini set at just over half distance stood as the benchmark for much of the remainder of the session, before Kornfeil guided his Prustel GP KTM to a 1:59.206s.
The Czech rider's time remained intact as the session ended, though he made a heavy impact with the barrier after running straight at Turn 12 on his final lap.
RBA's Rodrigo was two tenths adrift in second despite a fall at Turn 12 in the closing moments, while Bezzecchi rounded out the top three from Oettl and Martin.
Bastianini entered the final 15 minutes of FP2 setting the best pace of the day, first with a 1:59.204s, before improving to a 1:59.147s.
Martin, Nicolo Bulega on the Sky VR46 KTM and Rodrigo all led the session prior to Bastianini taking over, while Bezzecchi leaped up to second to shadow the latter with 10 minutes to go.
A further improvement from Bastianini to a 1:59.050s would follow, though Niccolo Antonelli would usurp him with two minutes remaining after the SIC58 rider fired in a 1:58.937s.
Martin soon deposed Antonelli, the Gresini rider edging ahead with a 1:58.804s, before a final effort of 1:58.418s cemented top spot for Bastianini.
Rordigo was once again second, while Bulega completed the top three. Martin was left in fourth after losing too much time in the final sector of his last lap.
Antonelli completed the top five from Aron Canet, who put in a late charge in FP2 having taken much of the day steady as he recovers from the injuries he sustained in his race crash at Misano.
Lorenzo Dalla Porta was seventh on the sister Leopard bike, with the second RBA machine of Kazuki Masaki eighth. The top 10 of the combined standings was rounded out by Kornfeil, who was declared fit to continue after his heavy FP1 fall, and Bezzecchi
